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.TH COMM 1 "Mar 3, 2004"
.SH NAME
comm \- select or reject lines common to two files
.SH SYNOPSIS
.LP
.nf
\fBcomm\fR [\fB-123\fR] \fIfile1\fR \fIfile2\fR
.fi

.SH DESCRIPTION
.sp
.LP
The \fBcomm\fR utility reads \fIfile1\fR and \fIfile2\fR, which must be ordered
in the current collating sequence, and produces three text columns as output:
lines only in \fIfile1\fR; lines only in \fIfile2\fR; and lines in both files.
.sp
.LP
If the input files were ordered according to the collating sequence of the
current locale, the lines written will be in the collating sequence of the
original lines. If not, the results are unspecified.
.SH OPTIONS
.sp
.LP
The following options are supported:
.sp
.ne 2
.na
\fB\fB-1\fR\fR
.ad
.RS 6n
Suppresses the output column of lines unique to \fIfile1\fR.
.RE

.sp
.ne 2
.na
\fB\fB-2\fR\fR
.ad
.RS 6n
Suppresses the output column of lines unique to \fIfile2\fR.
.RE

.sp
.ne 2
.na
\fB\fB-3\fR\fR
.ad
.RS 6n
Suppresses the output column of lines duplicated in \fIfile1\fR and
\fIfile2\fR.
.RE

.SH OPERANDS
.sp
.LP
The following operands are supported:
.sp
.ne 2
.na
\fB\fIfile1\fR\fR
.ad
.RS 9n
A path name of the first file to be compared. If \fIfile1\fR is \fB\(mi\fR, the
standard input is used.
.RE

.sp
.ne 2
.na
\fB\fIfile2\fR\fR
.ad
.RS 9n
A path name of the second file to be compared. If \fIfile2\fR is \fB\(mi\fR,
the standard input is used.
.RE

.SH USAGE
.sp
.LP
See \fBlargefile\fR(7) for the description of the behavior of \fBcomm\fR when
encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
.SH EXAMPLES
.LP
\fBExample 1 \fRPrinting a list of utilities specified by files
.sp
.LP
If \fIfile1\fR, \fIfile2\fR, and \fIfile3\fR each contain a sorted list of
utilities, the command

.sp
.in +2
.nf
example% \fBcomm -23 file1 file2  | comm -23 - file3\fR
.fi
.in -2
.sp

.sp
.LP
prints a list of utilities in \fIfile1\fR not specified by either of the other
files. The entry:

.sp
.in +2
.nf
example% \fBcomm -12 file1 file2 | comm -12 - file3\fR
.fi
.in -2
.sp

.sp
.LP
prints a list of utilities specified by all three files. And the entry:

.sp
.in +2
.nf
example% \fBcomm -12  file2 file3 | comm -23 -file1\fR
.fi
.in -2
.sp

.sp
.LP
prints a list of utilities specified by both \fIfile2\fR and \fIfile3\fR, but
not specified in \fIfile1\fR.

.SH ENVIRONMENT VARIABLES
.sp
.LP
See \fBenviron\fR(7) for descriptions of the following environment variables
that affect the execution of \fBcomm\fR: \fBLANG\fR, \fBLC_ALL\fR,
\fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
.SH EXIT STATUS
.sp
.LP
The following exit values are returned:
.sp
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 6n
All input files were successfully output as specified.
.RE

.sp
.ne 2
.na
\fB\fB>0\fR\fR
.ad
.RS 6n
An error occurred.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
CSI	enabled
_
Interface Stability	Standard
.TE

.SH SEE ALSO
.sp
.LP
.BR cmp (1),
.BR diff (1),
.BR sort (1),
.BR uniq (1),
.BR attributes (7),
.BR environ (7),
.BR largefile (7),
.BR standards (7)
